This invention relates in general to devices for delivering fluids at precise selected flow rates and, more particularly, to systems for providing multiple, precisely rate-controlled administrations of medical fluids to patients.
Medical fluids have long been administered in the treatment of both human and animal patients. Typically, medical liquids have been introduced intravenously through tubes connecting a supply container to a hypodermic needle. These liquids include, for example, blood, saline solutions, glucose solutions and solutions containing various pharmaceuticals. Similarly, tubes running from supply containers may be introduced into the stomach, generally through the nose and gullet to supply nutrients, pharmaceuticals and the like. In some cases, tubes may be threaded into the lung for the administration of gases, mists, etc. in the treatment of some conditions.
In the past, these fluids were generally contained in a bottle or limp plastic bag hung from a support above the patient, with the force of gravity causing the fluid to move through a tube to the patient. Generally, the rate of flow was controlled by a valve device variably pinching the tube. Flow rate control with this arrangement was rather crude due to variations in flow control setting, changes in container elevation, changes in fluid head level as the fluid is used, etc. These systems were not vary portable, generally requiring a wheeled stand for the container to maintain the container height during patient movement. The height of the container above the administration site would undesireably change as a patient moved from a bed to a wheelchair or to walking.
While these systems are still widely used, attempts have been made to overcome the limitations and problems with them. Attempts have been made to pressurize the supply container with an internal or external gas-filled bladder to transmit pressure to the fluid in the container. Pressure would tend to decrease, however, during use since as the bladder expanded, the internal pressure decreased proportionately. Also, changes in ambient temperature would change bladder pressure.
More recently, a number of complex systems for maintaining flow rate in the delivery of medical fluids have been proposed. For example, Metcalf in U.S. Pat. No. 4,043,332 proposes to pressurize a supply container to a higher than delivery pressure, then use a flow regulator to reduce pressure and provide the desired flow rate. However, this system is capable of only limited flow rate adjustment, flow rate must be manually gradually adjusted, and flow rate cannot be quickly and accurately changed among several pre-selected rates, leading to possible errors in flow rate. Also, this device must still be hung from a support near the patient.
Other complex systems for administering medical fluids are described by Krakauer et al in U.S. Pat. No. 3,375,824, Dancy in U.S. Pat. No. 3,640,276 and Adelberg in U.S. Pat. No. 3,640,277. While each has unique features, none disclose a system having the desirable ability to quickly and precisely change flow rates among several different rates and all are large and cumbersome. Serious safety problems may be encountered if these devices are inadvertently opened during operation.
Thus, there is a continuing need for an improved medical fluid delivery system capable of providing a number of precisely selected flow rates in a compact easily portable system, with improved safety in the event of errors in the use of the system.